The combustible behaviour of building materials containing natural fibres is a well-known problem that has existed for a very long time. Indeed, since wood and cob have a low fire resistance, man has developed alternative building materials mainly made of mineral materials such as stones, clay bricks, concrete, and mineral wools that are less combustible. However, the carbon footprint of such structures is high, on the one hand due to the energy needed for the production of such materials (such as cements, bricks, blocks, rock wools), and on the other hand due to the energy cost of transporting such reputedly heavy and dense materials from their production sites to the building sites where they are used.
By signing the Kyoto agreements, many countries are committed to reducing their greenhouse gas emissions by a factor of four between now and 2050. Thus, for example, European Directives henceforth impose energy consumption limits on new buildings. These energy consumption limits take into account the entire life cycle of the building: namely, the energy for producing the building materials, the energy for transporting them, the energy for assembling them, the energy consumption for heating (winter) and cooling (summer) the premises, the energy for the demolition of the building and the treatment and transport of the corresponding waste.
Thus, there are many architects and building designers who wish to use greater quantities of novel building materials comprising fibres of natural origin within the context of sustainable development. Indeed, these novel materials have an intrinsic carbon dioxide storage capacity since they are made up of a high percentage of organic matter. Moreover, these novel materials generally use little energy for their manufacture, they are light, they have a low heat capacity and they can have excellent thermal or sound insulation properties when they are used in a sufficient thickness. Their energy balance and their greenhouse gas footprint, per square meter built, are thus highly favourable over the life cycle of the building.
However, their combustible property is a curb on their use for obvious reasons of occupational safety of the premises, and their biodegradable property, attractive for the sustainable development aspect, poses serious problems with respect to the sensitivity of these materials to attacks by parasites and moulds which often result in an accelerated degradation of the structure.
Moreover, the occupation of these building by people or animals also requires a neutrality of the materials used with respect to the allergy risks or health risks promoted for example by fungi, acarids and parasites such as fleas or ticks.
A large number of treatments are proposed in order to fireproof these novel materials comprising natural fibres. Mention may for example be made of: brominated compounds (such as polybrominated aromatic compounds, in particular decabromodiphenyl ether and tetrabromobisphenol), compounds based on boron salts (such as borates and in particular the hydrated salts of boric acid), phosphorus-containing compounds (such as, in particular, zinc phosphate, ammonium phosphate, and magnesium, zinc or zirconium polyphosphonates), nitrogen-containing compounds (such as ammonium sulphates and ammonium halides), salts of metal (aluminium, antimony, zinc) compounds.
U.S. Pat. No. 4,182,681 discloses a fire retardant composition in powder form consisting mainly of alkaline compounds such as borax (hydrated Na2B4O7) 43 w. % base of boric acid, Ammonium sulphate ((NH4)2SO4) 31 w. %, Aluminium sulphate (Al2(SO4)3) 19 w. %, alkaline Sodium carbonate (Na2CO3) 4 w %, Silica gel 1.3 w. %.
US2009/320717 discloses an alkaline fire retardant composition comprising a carbonate salt (alkaline) and one additional salt such as Borax (Na2B4O7.5H2O) (also alkaline). The composition may comprise white sand along with Borax and Baking soda (example 2 respectively 40/40/20 parts, example 3 respectively 25/25/50 parts).
However, several of these fire-retardant compounds may present risks to the health of people handling these products during the manufacture of the building materials or to the health of the occupants of the buildings constructed with these compounds, or during the end-of-life treatment and recycling of the materials. Mention may for example be made of:                among the fire retardants based on boric acid and boron salts certain national or even regional regulations (for example of the European Union) are changing to a CMR (carcinogenic, mutagenic and reprotoxic) classification of these substances,        among brominated fire retardants: certain polybromobiphenyls or polybrominated diphenylethers which are the subject of regulatory restrictions in several regions of the world, moreover, the halogenated agents that generate acidic hydrogen halide fumes in the event of the thermal reutilization, as fuel, of the materials at the end of the life cycle,        among the metal compounds, heavy metals (i.e. those capable of forming insoluble sulphides when they are in oxidized form in the form of cations) may be volatilized in the combustion fumes during the reutilization, as fuel, of the materials at the end of the life cycle. These combustion fumes must then be treated, for example with activated carbon to lower their heavy metal contents so that the fumes can be discharged into the natural environment with no environmental risk.        
Among the components used as fungicide, mention may be made of organotin compounds, organometallic complexes, or the (ammonium, copper, zinc, etc.) salts of organic acids, sulphur-containing compounds (such as octylisothiazolinone).
Among the parasiticidal compounds, mention may be made of pyrethrins, set of natural substances derived from pyrethrum flowers, synthetic pyrethroids, benzoylureas, organophosphorus compounds and carbamates. These substances have the drawback of being neurotoxic both to parasites and to humans. These compounds should therefore be used with precaution in order to minimize the risks to the health of the staff manufacturing the treated materials, or the building construction staff, or the people occupying buildings comprising materials treated with such compounds.